Water soluble synthetic tanning agent for producing shrunken grain leather



United States Patent 3,477,801 WATER SOLUBLE SYNTHETIC TANNING AGENT FORPRODUCING SHRUNKEN GRAIN LEATHER Stanley A. Lipowski, Livingston, N.J.,assignor to Diamond Shamrock Corporation, a corporation of Delaware NoDrawing. Original application. Sept. 20, 1966, Ser. No. 580,616, nowPatent No. 3,423,452, dated Jan. 21, 1969. Divided and this applicationApr. 8, 1968, Ser.

Int. Cl. C14c 3/18 US. Cl. 8-94.24 4 Claims ABSTRACT OF THE DISCLOSUREThis application is a divisional application of Ser. No. 580,616,Lipowski, filed Sept. 20, 1966, now Patent No. 3,423,452.

The present invention relates to synthetic tanning agents for producingshrunken grain leather as well as processes for producing and using suchsynthetic tanning agents.

Shrunken grain leather is a type of leather which has a patterndeveloped on the hide by the action of the tanning agent. The shrinkingaction is most pronounced on the grain of the leather which is the mostsensitive part of the hide substance. The shrinking effect is visible onall of the corium of the hide and is characterized by a decrease in thetotal area of the hide. The shrunken grain pattern formed on the surfaceof leather by action of tanning agents is quite different from thepattern obtained by simple embossing. The pattern formed by shrinkingthe grain of the skin by tanning has a natural look contrary to thepattern obtained by simple embossing which has a definite artificiallook and very little eye appeal. The principal problem in producing ashrunken grain efiect on the skins or hides which are to be used formanufacturing shoe leather or other fashion leathers is to obtain anatural looking pattern uniformly distributed over all of the surfacearea. Furthermore, such pattern should have sufficient depth andpermanent features that the shrunken grain pattern will completelyrecover its appearance after the leather has been stretched and thestretch has been released. Snythetic tanning agents employed inproducing shrunken grain leathers besides effecting the shrinking of thegrain must be complete and satisfactory tanning agents for the leatherand must not impair the generally required standards of good grade upperleather. Such standards mean that the shrunken grain leather must havegood round feel, high tensile strength, high stitch tear strength andthe like.

Numerous attempts have been made in the prior art to produce a syntheticshrunken gain tanning agent which will meet all of the aboverequirements. However, none of the synthetic tanning agents developed todate has been completely satisfactory. The principal reasons for thedifiiculties which have been encountered in the development of synthetictanning agents for producing shrunken grain leathers are that any goodsynthetic tanning agent under proper management of tanning processes canproduce a shrinking effect on a skin or hide but none of the previouslydeveloped synthetic tanning agents has been able to satisfy all of therequirements that must be met in producing a satisfactory shrunken grainleather. Such agents generally produce shrunken grain leather having awild coarse grain, that is, the grain is highly irregular. Furthermore,the shrunken grain pattern is not uniform and does not completely coverthe entire surface area of the hide. The pattern has low depth and poorrecovery on stretching which means that the shrunken grain leather maysuperficially look satisfactory but when it is exposed to the drasticaction of shoe manufacturing machines and the like, the shrunken grainleather will partly or entirely lose its pattern. Since a shrunken grainleather must maintain its pattern during manufacture as well as duringuse, it is extremely important that the pattern has good recovery afterstretching or use.

Production of satisfactory shrunken grain leather is highly advantageousin tannery operations where shoe leather or other fashion leathers arebeing produced. In every tannery producing smooth upper grade leather,some of the stock is of poor quality and produces second grade leather.Such second grade leather results from natural defects in the skins orhides such as barbed wire scratches, skin defects caused by insectbites, brand marks, other injuries or defects. These defects are clearlyvisible in the finished leather, limit the usefulness of the finishedleather and represent a large loss in the cutting area. Obviously,second grade leather and products produced from second grade leathermust be sold at much lower prices. For a long time, it has been a majorproblem of upper leather tanners to find more effective methods toutilize the defective hides more to their advantage. Such defectivehides can be more effectively utilized when they are sorted from otherhides at some intermediate step in the tanning operation such as eitherafter liming or pickling or preferentially in the blue, that is, afterchrome tanning when the defects in the hides become more apparent. Ifthe defective hides are separated at such a point and then converted toshrunken grain leather with all of its desirable properties, theshrunken grain leathers can be sold as highly profitable fashionleathers. Furthermore, such defective hides are not converted to smoothupper leather with the attendant. losses in the cutting areas. It is tobe understood that effective utilization of defective hides in theproduction of shrunken grain leathers can be accomplished only if theshrinking effect obtained is of such a nature that it provides extremelygood coverage of all the defects in the hide and gives a leather whichhas a natural appearance, that is, distinctly different from theappearance of cheap embossed leather. Only a few of the synthetictanning agents suggested by the prior art have shown promise in theproduction of shrunken grain leather. Although these agents have beenable to produce more or less visible shrinking effects, none of theseagents has been able to meet all of the rigorous requirements forshrunken grain leather outlined above.

For example, a synthetic tanning agent is disclosed in Us. Patent No.3,010,779 as being useful in the production of shrunken grain leather.This synthetic tanning agent is based on a 4,4-dihydroxy diph-enylsulfone resin condensed with naphthalene sulfonic acid and formaldehydeand is in a very strong acid form, that is, the agent contains freesulfuric acid and other strong acids which are extremely injurious toleather. This agent cannot be neutralized to the pH range of about 2 toabout 5 which is normally used in tanning processes because the agentprecipitates from solution during neutralization. The net result is thatthis agent produces a shrinking effect on leather which is of a very lowquality and the pattern is coarse and not complete. The poor action ofthis synthetic tanning agent can be attributed to several factors. Theagent lacks free methylol groups, that is, unreacted methylol groupswhich provide the astringency required to shrink the grain surface. Theagent has low salt tolerance, that is, it precipitates in salt solutionscontaining low salt concentrations, that is, solutions containing aslittle as 1% by weight of sodium chloride. Thus, this agent on contactwith pickled stock which contains appreciable quantities of salt willprecipitate at an early stage during the tanning operation so that itsshrinking action on the grain will be lost. Precipitation from saltsolutions at these concentrations indicates that the agent is apolymeric material. Consequently, this agent is only able to act as atanning agent because it does not have sufiicient astringency to causeproper shrinking of the grain surface. Similar results have beenobtained with other synthetic tanning agents which are excellent tanningagents but do not have sufiicient astringency to cause rapid shrinkingof the grain before further penetration of the synthetic tanning agentinto the leather makes shrinking of the grain surface impossible.

It is an object of the present invention to provide synthetic tanningagents which will produce shrunken grain leathers which have deep, fineand uniform patterns, evenly distributed over the entire surface of theleather, have good recovery after stretching and have the otherrequirements of high fashion leathers. Another object of the presentinvention is to develop processes for producing synthetic tanning agentsfor use in the production of shrunken grain leathers. A further objectis to produce tanning processes employing such agents in the productionof shrunken grain leathers. Still another object is to produce shrunkengrain leathers. Other objects of this invention will become apparentfrom the detailed description given hereinafter. It is intended that thedetailed description and specific examples do not limit the presentinvention but merely indicate preferred embodiments thereof sincevarious changes and modifications within the scope of the invention willbecome apparent to those skilled in the art.

The above as well as other objects of the present invention have beenmost unexpectedly and successfully achieved in the following manner. Ihave discovered a new and novel class of water soluble synthetic tanningagents which are useful in producing shrunken grain leathers for use inupper shoe leather and other high fashion leathers. Furthermore, I havediscovered processes for producing such synthetic tanning agents.Additionally, I have found that use of these synthetic tanning agents inthe tanning of hides and skins consistently produce high quality uppershrunken grain shoe leathers, fashion leathers and the like which farexceed the shrunken grain leathers produced in the past.

I have found that such synthetic tanning agents must contain at least0.5 free methylol groups per mole of sulfone employed, that is, theunreacted methylol groups per mole of sulfone present in the synthetictanning agent if all of the desirable properties are to be obtained withthe agent in the production of shrunken grain leathers. Furthermore, Ihave discovered that it is essential for the synthetic tanning agent tobe substantially in monomeric form and that synthetic tanning agentsbased on polymeric forms or resins are to be avoided. Such polymericagents have poor shrinking action on leather. I have also found thatsuch tanning agents when in solution should not precipitate onneutralization at pHs from about to about 7. Such tanning agents can beneutralized with alkali metal hydroxides such as sodium hydroxide,potassium hydroxide, lithium hydroxide and the like, ammonium hydroxidelow molecular weight amines such as monomethylamine, dimethylamine,monoethanolamine, diethanolamine, triethanolamine, n-ethylamine,n-propylamine, their isomers and the like. Likewise, such tanning agentsshould not contain strong acids such as free sulfuric acid or the like.Furthermore, such tanning agent should be soluble in tanning solutionsor liquors containing at least 2.5% by weight of sodium chloride. Theimportance of such structural, chemical and physical requirements insynthetic tanning agents for use in the production of shrunken grainleathers was not appreciated or suggested by the prior art.

Briefly, the synthetic tanning agents disclosed in the present inventionare the reaction products of one mole of a sulfone having a purity offrom about to by weight such as 4,4'-dihydroxy diphenyl sulfone, 4,2-dihydroxy diphenyl sulfone, 2,2'-dihydroxy diphenyl sulfone or mixturesof these sulfones with from about 1.5 moles to about 5.0 moles offormaldehyde or formaldehyde liberating compositions per mole of sulfoneand from about 0.5 mole to about 2.0 moles of 2-naphthalene sulfonicacid per mole of sulfone with the proviso that the final reactionproduct contains at least 0.5 free methylol groups per mole of sulfone,that is, unreacted methylol groups per mole of sulfone employed, issoluble in salt solutions containing at least 2.5% by weight of sodiumchloride and when in solution does not precipitate on neutralization ata pH of from about 0 to about 7. Such synthetic tanning agents can alsobe the reaction products of (a) one mole of methylolated sulfone havinga purity of from about 95 to 100% by weight such as methylolated4,4'-dihydroxy diphenyl sulfone, methylolated 4,2-dihydroxy diphenylsulfone, methylolated 2,2'-dihydroxy diphenyl sulfone or their mixtureswherein one mole of the sulfone contains from about 1.5 to about 4 freemethylol groups and (b) from about 0.5 to about 2.0 moles of 2-naphthalene sulfonic acid per mole of sulfone with the proviso thatfinal reaction product contains at least 0.5 free methylol groups permole of sulfone employed, is soluble in salt solutions containing atleast 2.5% by weight of sodium chloride and when in solution does notprecipitate on neutralization at a pH of from about 0 to about 7.

These water soluble shrunken grain synthetic tanning agents can beprepared by reacting together at a temperature range of from about roomtemperature to about reflux temperature, an aqueous reaction mixturecontaining one mole of a sulfone having a purity of from about 95 to100% by weight selected from the group consisting of 4,4'-dihydroxydiphenyl sulfone, 4,2'-dihydroxy diphenyl sulfone, 2,2'dihydroxydiphenyl sulfone or their mixtures, from about 1.5 moles to about 5.0moles of formaldehyde or a formaldehyde liberating composition per moleof sulfone, from about 0.5 mole to about 2.0 moles of Z-naphthalenesulfonic acid per mole of sulfone and water with the proviso that thequantities of sulfone, aldehyde and Z-naphthalene sulfonic acid areselected within the molar range stated so that the final reactionproduct contains at least 0.5 free methylol groups per mole of sulfone,is soluble in salt solutions containing at least 2.5 by weight of sodiumchloride and when in solution does not precipitate on neutralization ata pH of from about 0 to about 7. Such products should contain little, ifany, unreacted naphthalene sulfonic acid. The temperature employed inthis process may vary from about 20 C. to about C. and when pressure isemployed may be as high as about C. The quantity of water employed isusually from about three to above five times the weight of the sulfoneemployed. The reaction mixture is relatively dilute and is sufficientlydilute to prevent any condensation of 2-naphthalene sulfonic acid withformaldehyde Which might lead to the formation of polymeric materials.The Z-naphthalene sulfonic acid in the initial stages of the reactionserves as a dispersant for the sulfone until methylolation of thesulfone begins. Once methylolation of the sulfone begins, a portion ofthe free methylol groups in the sulfone react with active hydrogen atomson the naphthalene ring of the naphthalene sulfonic acid to form thedesired synthetic tanning agent. The process is carried out by mixingthe required quantities of reactants and Water at room temperature andheating the resulting mixture to the reflux point which is usuallybetween 95 C. and 110 C. at atmospheric pressure. The mixture isrefluxed until a clear solution is obtained and the product has thefollowing properties. The final reaction product must contain at least0.5 free methylol groups per mole of sulfone employed. Furthermore,substantially all of the naphthalene sulfonic acid should be condensedwith the methylolated sulfone. The final product should be soluble insalt solutions containing at least 2.5% by weight of sodium chloride.Furthermore, the final product should not precipitate from solution onneutralization at pHs from about 0 to about 7. The final product shouldbe sufficiently neutralized so that it does not contain strong acidssuch as free sulfuric acid or the like. When the final product has theabove properties, it is then cooled to room temperature. The proceduredescribed above avoids bridging between dihydroxy diphenyl sulfonemolecules, other reactants or reaction product by reactions withformaldehyde which will produce polymeric materials. When desired, asolvent such as alcohol or any other solvent that does not interferewith the reactions involved in the process may be used in conjunctionwith water. Use of such solvent mixtures can be advantageous when higheror lower reflux temperatures are desired.

Alternatively, these water soluble shrunken grain synthetic tanningagents can be prepared by reacting together at a temperature range offrom about 50 to about 150 C. an aqueous reaction mixture containing onemole of a methylolated sulfone having a purity of from about 95% to 100%by weight such as methylolated 4,4'-dihydroxy diphenyl sulfone,methylolated 4,2'-dihydroxy diphenyl sulfone, methylolated2,2'-dihydroxy diphenyl sulfone or their mixtures wherein the sulfonecontains from about 1.5 to about 4 free methylol groups per mole ofsulfone employed, from about 0.5 mole to about 2.0 moles ofZ-naphthalene sulfonic acid per mole of sulfone and water with theproviso that the quantities of methylolated sulfone and Z-naphthalenesulfonic acid are selected within the molar ranges stated so that thetanning agent contains at least 0.5 free methylol group per mole ofmethylolated sulfone employed, is soluble in salt solutions containingat least 2.5% by weight of sodium chloride and when in solution does notprecipitate on neutralization at a pH of from about 0 to about 7. Thequantity of water employed in this process may vary. Usually from aboutone and one-half to about two times the weight of sulfone of water isemployed in the methylolation step and from about one-half to two timesthe weight of the sulfone of water is employed in the condensationprocess. The heating of the reaction mixture at the aforementionedtemperatures, or preferably at reflux temperature, that 1s, about 95 C.to about 110 C. is carried out until a clear solution is obtained. Ifdesired, the condensation can be carried out under pressure or in thepresence of solvents at temperatures as high as about 150 C. Thereaction product, that is, the water soluble shrunken gram synthetictanning agent should have the following properties. The final reactionproduct must contain at least 0.5 free methylol group per mole ofsulfone employed. Furthermore, substantially all of the naphthalenesulfonic acid should be condensed with the methylolated sulfone. Thereaction product should be soluble in salt solutions containing at least2.5% by weight of sodium chloride. Further, the reaction product shouldnot precipitate from solution on neutralization at pI-ls from about 0 toabout 7. The final product should be sufficiently neutralized so it doesnot contain strong acids such as free sulfuric acid or the like.

The number of free methylol groups per mole of sulfone in either thedimethylolated sulfone or the synthetic tanning agents described abovecan be determined by the De Jong method which is described in Rec. trav.chim. 72: 653, 654 (1953).

Methylolation of the sulfone Methylolation of the sulfone can beachieved in the following procedure which avoids bridging betweendihydroxy diphenyl sulfone molecules during methylolation. When bridgingoccurs, the resulting polymeric materials are partially methylolatedsulfone resins, which on acidification separate as gummy materials andare not crystalline solids which can be separated easily byacidification and washed by decantation. Prior to methylolation, thedihydroxy diphenyl sulfone is reacted with sodium hydroxide in suchproportions that both of the hydroxyl groups in the phenol rings areconverted to the corresponding sodium salts. At this point, the sulfoneshould be water soluble and have a pH of from about 9.5 to about 10.0.The disodium salt of the sulfone is then reacted with suificientformaldehyde to obtain the desired methylolated sulfone. Usually fromabout 1.5 moles to about 5.0 moles of formaldehyde or a formaldehydeliberating composition per mole of sulfone is employed. Methylolationtakes place at moderate temperatures such as about 20 C. to about 55 C.over an extended period of time. For example, methylolation at about 45C. to about 55 C. will require from about 16 hours to about 30 hours.The methylolation reaction mixture can be analyzed by determining theamount of formaldehyde remaining in the mixture by the method describedin Example III below. This method determines the amount of formaldehyderemaining in the reaction mixture after methylolation. The methylolationreaction mixture can also be analyzed by the De Jong method describedabove. The De Jong method determines the number of free methylol groupspresent in the methylolated sulfone. When the De Jong method isemployed, the unreacted formaldehyde should be removed from the reactionmixture before the number of methylol groups per mole of sulfone isdetermine. After methylolation is complete, the methylolated dihydroxydiphenyl sulfone is recovered in the form of a solid precipitate byprecipitation with an acid such as hydrochloride, sulfuric or the like.The salts formed during the acidification are water soluble and can beeasily removed from the methylolated dihydroxy diphenyl sulfoneprecipitate by simple decantation and washing. After the methylolatedsulfone has been separated from the reaction mixture as a solid andwashed free of salts, unreacted formaldehyde, formaldehyde liberatingcompositions and the like, it is reacted in aqueous solution with therequired quantity of Z-naphthalene sulfonic acid at a temperature offrom about 55 C. to about 150 C. to obtain a synthetic tanning agenthaving the properties described above. The methylolated sulfone to beuseful in the present invention should have a purity of about by weightto by weight and should contain from about 1.5 to about 4 free methylolgroups per mole of sulfone employed. The methylolated sulfone may bemethylolated 4,4'-dihydroxy diphenyl sulfone, methylolated 4,2-dihydroxydiphenyl sulfone, 2,2'-dihydroxy diphenyl sulfone or mixtures thereof.The impurities in the methylolated sulfone include methylolatedpolymeric sulfone, methylolated phenol sulfonic acids, other byproductsand the like.

The dihydroxy diphenyl sulfone or mixture of sulfones employed in theprocesses disclosed in this invention must be of high purity. It shouldhave a purity of about 95% to 100% by weight of 4,4'-dihydroxy diphenylsulfone, 4,2-dihydroxy diphenyl sulfone, 2,2'-dihydroxy diphenyl sulfoneor their mixtures and should not contain more than 5% by weight ofimpurities such as polymeric sulfones, phenol sulfonic acids, otherbyproducts or the like. A procedure for preparing a dihydroxy diphenylsulfone having satisfactory properties is described in Example I below.It is to be understood that any known method which produces dihydroxydiphenyl sulfone isomers or mixtures thereof having purities from. about95% by weight to 100% by weight can be employed in the presentinvention.

Formaldehyde or formaldehyde liberating compositions can be used in thepreparation of the synthetic tanning agents and methylolated sulfonesdisclosed in the present invention. For example, formaldehyde can beused in the form of 10% to 40% aqueous solution, 30% to 55% alcoholicsolutions with alcohols such as metha- I101, n-butanol, i-butanol or thelike. Formaldehyde can also be used in the form of a formaldehydeliberating composition such as its polymeric forms such asparaformaldehyde, trioxane, or the like. It is also to be understoodthat such formaldehyde liberating compositions include any form such asan acetal which is capable of producing formaldehyde such as acetals andthe like.

The synthetic tanning agents and their use The synthetic tanning agentsproduced by the processes described above are analyzed by the De Jongmethod referred to above to determine if they contain at least 0.5 molesof free methylol groups per mole of sulfone employed. When desired, thetanning agents may contain as may as 3 free methylol groups per mole ofsulfone employed in the process. Furthermore, the tanning agent shouldbe neutralized to the point where all of the free sulfuric acid presentin the naphthalene sulfonic acid employed in the process is completelyneutralized and any free, unreactul Z-naphthalene sulfonic acidremaining in the synthetic tanning agent is present only in an amountsufficient to give a pH of from about to about 7 in the finishedsynthetic tanning agent. For most purposes, about 90% of theZ-naphthalene sulfonic acid groups, after reaction of the naphthalenesulfonic acid with the methylolated dihydroxy diphenyl sulfone, areneutralized. The presence of unneutralized sulfuric acid or othersources of high acidity in the finished synthetic tanning agent ishighly undesirable because such acidity contributes substantially to thecoarseness of pattern produced when the synthetic tanning agent isemployed in shrunken grain tanning. Furthermore, the synthetic tanningagents produced by the process disclosed in this invention should besoluble in water at any dilution, soluble in salt solutions containingat least 2.5% by weight of sodium chloride. Likewise, the tanning agentshould not reci itate from solutions on neutralization to pHs of fromabout 0 to about 7.

The synthetic tanning agents disclosed in this invention are useful inproducing shrunken grain effects on animal skins such as cowhides,calfskins, goatskins, horsehides, reptile skins, other animal skins orthe like. The term skin is used to include any animal skin or hide whichcan be used in the production of shrunken grain leather. As examples ofskins which may be employed in the production of shrunken grain leather,there may be mentioned skins of freshly killed animals, limed skins,pickled skins, partly tanned skins, partly dechromed skins, dechromedskins and the like. Generally from about by weight to about 50% byweight based on the Weight of the skins of the synthetic tanning agentis employed. By the term synthetic tanning agent is meant the solutionof the solid reaction products, salts and the like obtained by theprocesses disclosed in this invention. The synthetic tanning agentgenerally contains from about 15% by weight to about 50% by weight ofsolid reaction products. Usually from about 30% by weight to about 100%by weight based on the weight of skins 0r hides of water is added to thesynthetic tanning agent solution to prepare the tanning solution orliquor. Shrunken grain leathers are produced by drumming the synthetictanning agent into the animal skin. The synthetic agent is used in formof a solution or liquor and is drummed into the skin at a temperature offrom about 70 F. to about 90 F. for about two hours to about twelvehours. Exhaust of the synthetic tanning agent from the tanning solutionor liquor at the end of the drumming process is essentially complete,that is, the tanning agent is absorbed in the skin and little if any ofthe tanning agent remains in the tanning solution or liquor.

Shrunken grain leather produced by synthetic tanning agents disclosed inthis invention can be used in the manufacture of upper shoe leather,garment leather, handbag leather, high fashion leather and the like.When the synthetic tanning agents are used in connection with vegetabletannages, moccasin type leather can be produced.

The synthetic tanning agents of this invention can be combined not onlywith chrome tannages but with other tannages such as zirconium tannagesand the like. When chrome stock is used in the production of shrunkengrain leathers, the leather is dechromed prior to use. The dechromingprocess can be varied over wide limits by using chemicals and/ormaterials which complex easily with chromium and facilitate its removalfrom the chrome tanned leather. Materials useful in dechroming leatherinclude complexing acids such as oxalic, tartaric, citric, phosphoricacid or salts of such acids, e.g., Rochelle salt and the like, chelatingagents such as ethylenediaminetetracetic acid, hydroxamic acids,amidoximes or the like. Such dechroming agents are applied in sufficientquantities to dechrome the stock to the point where its shrinkagetemperature in boiling water drops from about 212 F. to about 110 F.Processing conditions employed during dechroming .must be controlledcarefully so that the internal structure of the leather is not damaged.After the leather is dechromed, the stock must be promptly washed withsalt water to avoid acid swelling. The resulting washed dechromed stockis then used in the shrunken grain process in the same manner as pickledskins or other forms of stock.

When the tanning agents of the present invention are employed in theproduction of shrunken grain leathers, the mechanical action encounteredin the drumming and other plant operations which promote the shrinkingeffect of the synthetic tanning agents must be controlled carefully. Forexample, the speed of the drums must not be exaggerated in order toprevent overheating of the stock. The temperature during the shrinkingprocess must be carefully controlled and kept as low as possible.Usually temperatures in the range of from about F. to about F. areemployed. The rotating drums .must be stopped at certain time intervalsduring the process so that they can be aired off and allowed to coolbefore the temperature of the stock reaches the critical uppertemperature limit of about 90 F. Extensive damage can be done to thestock which will render it useless as leather unless these precautionsare taken. The amount of synthetic tanning agent solutions employed inshrunken grain tanning will be from about 15% to about 50% by weight (asis) based on the weight of the stock.

Shrunken grain leather obtained by the processes disclosed in thisinvention shows undiminished strength after it is rechromed. Theshrunken grain leather can be rechromed with from about 1 /2 to about 2/2% chromic oxide based upon the weight of the stock. The startingbasicity during rechroming can be as low as 33% to 50% Schlorlemmerdegrees which corresponds to a basicity of 4/12 to 6/12. The lowerbasicity chrome liquors can be subsequently made more basic by theaddition of alkalis such as sodium bicarbonate, ammonium bicarbonate orthe like. Although higher basicity liquors do not require basicityadjustments, their action is more drastic and their use must be morecarefully controlled. It is particularly important that care is takennot to overheat the stock during the rechroming process. The shortfloats and high basicity of the liquors in conjunction with themechanical action of the rotating drums can easily cause severe damageto the hides in rechroming if the stock temperature is permitted to riseabove temperatures of about 90 F. or higher. Generally, the shrunkengrain stock is rechromed to a point where its shrinkage point is broughtup to a minimum temperature of about 205 F. Generally, shrinkagetemperatures of from about 210 F. to about 212 F. are the mostdesirable.

When stock such as pickled stock or dechromed stock is tanned with thesynthetic tanning agents of this invention, complete exhaust of thesynthetic tanning agent is observed. Complete exhaust demonstrates thehigh aflinity which the tanning agent has for the hide substance. Spentliquors from shrunken grain tanning processes in which the synthetictanning agents of this invention are used contain little if any of thetanning agents. This is highly desirable as little if any of the agentsare lost during the tanning processes. The concentration of synthetictanning agents in the spent liquors can be determined by conventionalmethods such as the Oflicial Hide Powder Method and the like.

For a fuller understanding of the nature and objects of this invention,reference may be made to the following examples which are given merelyto illustrate the invention and are not to be construed in a limitingsense. All weights, proportions and percentages are by weight unlessotherwise indicated. Likewise all temperatures are C., unless otherwiseindicated.

EXAMPLE I (A) Preparation of a dihydroxy diphenyl sulfone 1148 g. (12.2moles) of phenol, 612 g. (6 moles) of sulfuric acid (96% by weightactive) and 125 g. monochlorobenzene were charged into a reaction vesselequipped with an agitator and a water separation trap. The reactionmixture was heated to the reflux temperature which was about 140 C. Theescaping vapors of chlorobenzene and water formed during the reactionwere condensed in the condenser and were separated in the trap. The drychlorobenzene was returned to the reaction mixture. Reaction temperaturewas gradually increased to a temperature between 165 C. and 170 C. Afterfrom about 210 cc. to 215 cc. of water had been separated by azeotropicdistillation, the reaction mixture was titrated to determine itsacidity. A 10 g. sample of the reaction mixture at this point should notrequire more than 19.00 cc. to 20.00 cc. of 0.5 N sodium hydroxidesolution to neutralize the sample to a pH of 7.0 This titer showed thatover 75 per cent of the reactants have been converted to dihydroxydiphenyl sulfone. Higher conversion would require higher temperaturesand longer times with the resulting resinification of the sulfone.Titers in above mentioned range have been found to be satisfactory inthat they avoid resinification and provide satisfactory conversion todihydroxy diphenyl sulfones.

After the desired acidity was obtained, 500 cc. of water was addedcarefully to the reaction product. The reaction product was thenneutralized to a pH between and 6 by the cautious addition of from about120 g. to about 130 g. of 50% by weight sodium hydroxide solution.Approximately 1,000 cc. of Water was then added to the reaction productand the resulting mixture was azeotropical- 1y distilled to remove thechlorobenzene. The chlorobenzene was removed from the water and thewater returned to the reaction mixture. After all of the chlorobenzenewas stripped from the reaction mixture, an additional 1,000 cc. of waterwas added and the resulting solution of the reaction product was heatedto its boiling point. A clear solution was obtained at the boilingpoint. The solution contained the reaction product dissolved in about2,500 cc. of boiling water.

The clear solution was then transferred to a reaction vessel containingapproximately 4,000 cc. of boiling water and the resulting dilutedsolution was allowed to cool slowly to room temperature with vigorousagitation. Dihydroxy diphenyl sulfone precipitated in the form of creamcolored crystals from the solution on cooling to room temperature. Thecrystals were removed by filtration or centrifugation or were left inthe crystallization vessel and were then washed several times with coldwater until the crystals were free of residual salts. The resultingdihydroxy diphenyl sulfone crystals were then either dried or left inthe form of a wet paste for use in further reactions. The dihydroxydiphenyl sulfone crystals were analyzed for isomer distribution by theprocedure given in Example I of U .S. Patent No. 2,833,828-Sauls (May 6,1958). The crystals were found to have a purity of 98% by weight and aweight ratio of 88% of 4,4-dihydroxy diphenyl sulfone isomer to 12% of4,2'-dihydroxy diphenyl sulfone. The 2% by weight of impurities in themixture consisted of polymeric sulfones, phenol sulfonic acids, otherbyproducts and the like.

(B) Recrystallization of dihydroxy diphenyl sulfone When desired orrequired, the crystalline dihydroxy diphenyl sulfone isomer mixtureobtained in part (A) above was further purified by the followingprocedure. The crystalline material was suspended in twenty times itsweight of water and heated to the boiling point. The crystallinematerial dissolved at the boiling point and a clear solution wasobtained. 0.1% by weight of decolorizing carbon and 0.5% by weight offilter aid were added to the boiling mixture. The mixture was thenstirred for about five minutes and filtered at its boiling point toremove the decolorizing carbon, filter aid and other impurities. Theclear, decolorized solution of dihydroxy diphenyl sulfone isomers wasthen cooled slowly to room temperature with vigorous agitation. Crystalsof the dihydroxy diphenyl sulfone isomers separated on cooling to roomtemperature and were removed by filtration. The recrystallized dihydroxydiphenyl sulfone isomer mixture was in the form of pure white crystals.It was approximately 100% by weight pure. The isomers were present in aweight ratio of 88% of the 4,4-dihydroxy diphenyl sulfone isomer to 12%of the 4,2-dihydroxy diphenyl sulfone isomer. It is to be understoodthat purification of the dihydroxy diphenyl sulfone by recrystallizationis not generally required in the preparation of the synthetic tanningagents of this invention for most tanning processes.

EXAMPLE II Preparation of a Z-naphthalene sulfonic acid solution 128 g.(1 mole of naphthalene and 160 g. (1.6 mole) of sulfuric acid (98% byWeight active) were mixed together in a reaction vessel at roomtemperature. The resulting reaction mixture was heated rapidly to 150 C.and agitated for three hours at 150 C. The resulting reaction productwhich was a mixture of Z-naphthalene sulfonic acid and sulfuric acid wascooled to C. and sufiicient cold water was added to obtain aZ-naphthalene sulfonic acid-sulfuric acid mixture having an activity ofabout 75% by weight. This mixture was then cooled to room temperature.The mixture contained one mole of 2-naphthalene sulfonic acid and 0.6mole of sulfuric acid.

EXAMPLE III Preparation of a synthetic tanning agent 159 g. of a drycrystalline dihydroxy diphenyl sulfone isomer mxture, containing 98% byweight of sulfones having an isomer weight ratio of 88% of the4,4-dihydroxy diphenyl sulfone isomer to 12% of the 4,2'-dihydroxydiphenyl sulfone isomer and 2% by weight of impurities consisting ofpolymeric sulfones, phenol sulfonic acids, other byproducts and the likeas described in part (A) of Example I above, 156 g. water and 100 g.(1.25 moles) of 50% by weight sodium hydroxide solution were mixedtogether and heated until a clear solution was obtained. The mixture ofsulfone isomers used in this example weighed 156 g. (0.625 moles). Theresulting clear solution was cooled to about 50 C. and 106 g. (1.307mole) of form-aldehyde (37% by weight active) was added. The molar ratioof formaldehyde to dihydroxy diphenyl sulfone was 1.307/ 0.625 or 2.09.This reaction mixture was stirred at a constant temperature of 50 C. for24 hours. As reaction proceeded, the initially clear solution becamemilky in appearance.

After reaction for 24 hours at 50 C. a sample of the reaction mixturewas titrated by a modified sodium bisulfite method to determine itsformaldehyde content. Briefly, this method involved addition of a 5 g.sample of the reaction mixture to 50 cc. of a 10% by weight sodiumchloride solution. Sulfuric acid (98% by Weight active) was then addedto obtain a pH of about 5. A precipitate formed and was removed byfiltration. The filtrate was collected and then neutralized to a pH of7.0. 50 cc. of a l M sodium sulfite solution was added. Whenformaldehyde was present in the filtrate, the pH of the filtrate wasabove 9. The filtrate was then back-titrated with 0.5 N hydrochloricacid solution to a pH of 9.0. When formaldehyde was not present, the pHof the filtrate after bisulfite addition was 9 and back-titration with0.5 N hydrochloric acid was not required. The percentage of formaldehydepresent in the filtrate was then calculated by the following formulaWeight of sample wherein cc. HCl represents the quantity of 0.5 Nhydrochloric acid required to back-titrate to a pH of 9. Theformaldehyde content of the preparation described in this example wasfound to be 1.65% by weight. The concentration of formaldehyde presentinitially in the reaction mixture was 7.53% by weight which meant that5.88% by weight of formaldehyde of 78.1% of the total formaldehydeemployed initially in the reaction reacted. This formaldehyde usagemeant that 1.02 mole of formaldehyde reacted with the phenolic ringspresent in the dihydroxy diphenyl sulfone, or in other words, the ratioof free methylol groups per mole of dihydroxy diphenyl sulfone was 163free methylol groups per mole of dihydroxy diphenyl sulfone.

After the formaldehyde analysis, the reaction mixture was cooled toabout 10 C. 250 cc. of cold water and 190 g. of sulfuric acid (33.5% byweight active) were added with cooling. The resulting mixture whichcontained a precipitate of methylolated dihydroxy diphenyl sulfone in awater and salt solution was decanted to remove the solution of water,unreacted formaldehyde and salt from the methylolated dihydroxy diphenylsulfone crystals. The precipitated methylolated dihydroxy diphenylsulfone crystals were then washed three times with 600 cc. portions ofcold water and each cold water wash was removed by decantation. Theformaldehyde content of the wash water obtained from the third wash anddecantation was analyzed by the procedure described above and found tobe 0.0% by weight. The pH of the third wash water was 5.4. After all ofthe formaldehyde had been removed by washing, the number of methylolgroups per mole of sulfone in the methylolated sulfone crystals wasdetermined by the De Jong method as described in Rec. trav. chim 72:653, 654 (1953). The methylolated sulfone was found to contain 1.6 freemethylol groups per mole of sulfone. The reaction mixture was 98% byweight pure and contained 2% by weight impurities. The weight ratio ofisomers in the crystals was 88% of methylolated 4,4-dihydroxy diphenylsulfone to 12% of methylolated 4,2'-dihydroxy diphenyl sulfone isomers.The 2% by weight of impurities included methylolated polymeric sulfones,methylolated phenol sulfonic acids, other byproducts and the like.

247.5 g. of Z-naphthalene sulfonic acid mixture (about 75% by weightactive) which contained 0.71 mole of 2- naphthalene sulfonic acid andwas prepared by the procedure in Example II above and 25 cc. of waterwere added to the wet, washed methylolated dihydroxy diphenyl sulfonecrystals obtained above. The resulting reaction mixture was heated toreflux. Reflux temperature was about 110 C. After heating for five hoursat reflux, 400 cc. of cold water was then added to the reaction mixtureand the mixture neutralized under cooling by the addition of 105 g. of50% by weight sodium hydroxide solution. The resulting neutralizedsolution was slightly hazy. 35 g. of isopropyl alcohol was added and thesolution cleared immediately. The pH of the clear solution was 2.2 asis. The solution, which was a synthetic tanning agent, contained 34.5%by weight of solids. The pH of the solution when diluted with distilledwater to 1% by weight solids was 4.4. The solution, which contained34.5% by weight solids, was soluble at all proportions in water and wassoluble in a 2.5% by weight sodium chloride solution. Furthermore,

the agent did not precipitate from solution on neutralization at pHsbetween about 0 and about 7. The number of free methylol groups in thesynthetic tanning agent as determined by the above-mentioned De Jongmethod was found to be 0.6 free methylol groups per mole of sulfoneemployed in the agent.

EXAMPLE IV Preparation of a synthetic tanning agent 154 g. of adihydroxy diphenyl sulfone paste mixture prepared by the proceduredescribed in part (A) of Example I above was mixed with g. of water and75 g. (0.94 mole) of 50% by weight sodium hydroxide solution and heateduntil a clear solution was obtained. 114 g. (1.41 mole) of formaldehydesolution (37% by weight) was added at 50- C. and the mixture was stirredat 50 C. for 24 hours. The sulfone parts employedv in this examplecontained 78% by weight of solids, the solids being 98% by weight of amixture of pure sulfone isomers and 2% by weight of impurities. Themixture of sulfone isomers weighed 117.5 g. (0.47 mole). The sulfoneisomers in the mixture were present in a weight ratio of 88% of the4,4'-dihydroxy diphenyl sulfone isomer to 12% of the 4,2-dihydroxydiphenyl sulfone isomer. The 2% by Weight of impurities in the mixtureconsisted of polymeric sulfones, phenol sulfonic acids, other byproductsand the like. The molar ratio of formaldehyde to dihydroxy diphenylsulfone in this reaction mixture was 3 moles of formaldehyde to 1 moleof dihydroxy diphenyl sulfone. After reaction for 24 hours at 50 C. asample of the reaction mixture was titrated for its formaldehyde contentby the procedure described in Example III above and found to contain2.23% by weight of unreacted formaldehyde. The initial formaldehydecontent of the reaction mixture was 9.95% by weight. In other words,7.72% by weight of formaldehyde, which represented 77.6% of the totalamount of formaldehyde used was consumed in the reaction. Thisformaldehyde usage represented reaction of 1.09 moles of formaldehydewith 0.47 mole of dihydroxy diphenyl sulfone, that is, the formaldehydereacted with the phenolic rings present in the sulfone. The ratio offree methylol groups to moles of dihydroxy diphenyl sulfone was 2.32free methylol groups per mole of dihydroxy diphenyl sulfone. Aftermethylolation, 200 cc. of cold water was added to the reaction mixtureand the reaction mixture was cooled to 10 C. A solution containing 50 g.of sulfuric acid (96% by Weight active) and g. of water was added to thereaction mixture with good cooling. The methylolated dihydroxy diphenylsulfone separated from the reaction mixture on cooling to 10 C. and theresulting slurry contained crystals of the methylolated dihydroxydiphenyl sulfone and a solution of unreacted formaldehyde, salt andother impurities. The slurry was cooled to 10 C. and the crystals ofdimethylolated sulfone allowed to settle. The solution containing theimpurities was removed from the crystals by decantation. The crystals ofmethylolated dihydroxy diphenyl sulfone were then washed three timeswith 500 cc. portions of cold water. The slurry was externally cooledwith ice during washing and decantation. After each addition of washwater, the crystals were slurried, allowed to settle and the wash waterwas decanted from the cooled slurry. The formaldehyde content of thelast wash water was analyzed by the procedure described in Example IIIabove and found to be 0.0%. The pH of the'last wash water was 3.8. Thewashed methylolated sulfone crystals were analyzed by the abovedescribed De Jong method and found to contain 2.32 free methylol groupsper mole of sulfone. The crystals were found to be 98% by weight pureand to contain 2% by weight of impurities. The weight ratio of theisomers in the crystals was 88% of methylolated 4,4-dihydroxy diphenylsulfone to 12% of methylolated 4,2-dihydroxy diphenyl sulfone. The 2% byweight of impurities in the crystals consisted of methylolated polymericsulfones, methylolated phenol sulfonic acids, other byproducts and thelike.

18.7.5 g. of Z-naphthalene sulfonic acid mixture (about 75% by weightactive) which contained 0.54 mole of Z-naphthalene sulfonic acid and wasprepared by the procedure given in Example II above, and 9 g. of waterwere added to the washed methylolated dihydroxy diphenyl sulfonecrystals and the resulting reaction mixture was refluxed for hours atabout 110 C. After refluxing for five hours, the reaction mixture wascooled to room temperature. 250 cc. of water was then added to thecooled mixture and the mixture was neutralized to a pH of 2.5 with 80 g.of 50% by Weight sodium hydroxide solution. The resulting product was ashrunken grain synthetic tanning agent in the form of a light yellowcolored clear syrupy solution. This solution contained 36% solids. Thesolution was clear and soluble when it was mixed with a 3% by weightsodium chloride solution. The tanning agent did not precipitate fromsolution on neutralization at pHs of from about 0 to about 7. Thesynthetic tanning agent was analyzed by the De Jong method and found tocontain 1.1 free methylol groups per mole of sulfone employed.

EXAMPLE V An alternate procedure for producing a shrunken grainsynthetic tanning agent 204 g. of dihydroxy diphenyl sulfone pasteprepared by the procedure described in part (A) of Example I above wascharged into a reaction vessel. The paste contained 78% by weight ofsolids, the solids being 98% by weight of a mixture of pure sulfoneisomers and 2% by weight of impurities. The mixture of sulfone isomersweighed 156 g. (0.625 mole). The sulfone ismoers in the mixture werepresent in a weight ratio of 88% of the 4,4- dihydroxy diphenyl sulfoneisomer to 12% of the 4,2- dihydroxy diphenyl sulfone isomer. The 2% byweight of impurities in the mixture consisted of polymeric sulfones,phenol sulfonic acids, other byproducts and the like. 407 g. of water,250 g. of Z-naphthalene sulfonic acid mixture (about 75% by weightactive) which contained 0.71 mole of Z-naphthalene sulfonic acid and wasprepared by the procedure described in Example II above and 101 g. (1.25mole) of formaldehyde solution (37% by weight active) were then chargedinto the reaction vessel and were mixed at room temperature. The molarratio of formaldehyde to dihydroxy diphenyl sulfone isomers in themixture was two moles of formaldehyde per mole of dihydroxy diphenylsulfone. The reaction mixture was heated to the reflux point, that is,about 102 C. and became a clear solution immediately. The reactionmixture was refluxed at 102 C. for 15 hours, cooled to room temperatureand neutralized with cooling by the addition of 106.5 g. of 50% byweight sodium hydroxide solution and 50 g. of water. The product of thereaction was about 1100 g. of a clear syrupy liquid containing 35%solids by weight. The clear syrupy liquid was the desired synthetictanning agent. The properties of the synthetic tanning agent werecomparable to those of the agent obtained in Example III above. That is,the tanning agent was soluble in salt solutions containing at least 2.5%by weight of sodium chloride and the agent did not precipitate fromsolution on neutralization at pHs from about 0 to about 7. Analysis ofthe synthetic tanning agent by the De Jong method showed that itcontained 1.0 free methylol groups per mole of sulfone employed.

EXAMPLE VI A synthetic tanning agent was prepared according to theprocedure described in Example I of US. Patent No. 3,010,779, wassynthesized and evaluated in the following manner.

255 g. of a dry 98% by weight pure crystalline dihydroxy diphenylsulfone isomers mixture prepared by the procedure given in part (A) ofExample I above, 150 g. of water and 35 g. of 45% by weight sodiumhydroxide solution were charged into a reaction vessel and mixed. Thesulfone isomer mixture contained 98% by weight of sulfone isomers and 2%by weight of impurities. The mixture of sulfone isomers weighted 250 g.(1.0 mole). The sulfone isomers in the mixture were present in a weightratio of 88% of the 4,4'-dihydroxy diphenyl sulfone isomer to 12% of the4,2'-dihydroxy diphenyl sulfone isomer. The 2% by weight of impuritiesin the mixture consisted of polymeric sulfones, phenol sulfonic acidsand the like. 87.5 g. (0.88 mole) of formaldehyde solution (30% byweight active) was then charged into the reaction vessel and theresulting reaction mixture was heated at its boiling point for 3 hours"to obtain a condensation product. The resulting condensation productwas then mixed with 275 g. (1.12 mole) by weight of the naphthalenesulfonic acid obtained by the procedure described in US. Patent No.1,972,754 and the mixture was reacted by heating at 120 C. for 1.5hours. When an attempt was made to neutralize the reaction product ofthis mixture with 50% sodium hydroxide solution, the synthetic tanningagent precipitated. Analysis of the synthetic tanning agent by the DeJong method showed that it contained 0.0 free methylol groups per moleof sulfone employed.

This example demonstrated that synthetic tanning agent prepared inaccordance with this procedure could not be satisfactority neutralizedto a pH in range of about 0 to about 7 so that the free sulfuric acidwas completely neutralized and the naththalene sulfonic acid waspartially neutralized. During the neutralization when only a fraction ofthe free sulfonic acid was neutralized, precipitation of the tanningagent began and became increasingly heavy as the pH was raised graduallyabove 0. Further, the agent was not soluble in a salt solutioncontaining 0.1% by weight of sodium sodium chloride.

EXAMPLE VII This example demonstrates the preparation of a synthetictanning agent from a crude and impure dihydroxy diphenyl sulfone.

162 g. (1.72 mole) of phenol, 87 g. (0.85 mole) of sulfuric acid (967 byweight active) and 50 g. of monochlorobenzene were mixed together in areaction vessel and heated to a maximum temperature of about 168 C. Thewater formed during reaction was removed by azeotropic distillation.After the dihydroxy diphenyl sulfone was formed, the reaction mixturewas neutralized with a solution containing 110 g. of 50% by weightsodium hydroxide solution and 300 g. of water. Monochlorobenzeneremaining in the reaction mixture was removed by azeotropicdistillation. After all of the monochlorobenzene had been removed, thereaction mixture was cooled to 20 C. and a suspension of white crystalsin a pink mother liquor was obtained. The suspension of crystals inmother liquor was then used directly without any purification or removalof mother liquor. This suspension was found to contain 0.6 mole ofsulfone isomers, that is, it contained 70% by weight of a mixture of4,4-dihydroxy diphenyl sulfone and 4,2'-dihydroxy diphenyl sulfoneisomers. The 30% by weight of impurities in the mixture includedpolymeric sulfones, phenol sulfonic acids, other byprodnets and thelike.

g. (1.23 mols) of formaldehyde (37% by weight active) was added to thesuspension of the crystals in the mother liquor and the resultingmixture stirred for 1 hour and 25 minutes at 24 C. The reactiontemperature was then gradually raised to 55 C. The mixture was thenreacted at 50 C. to 55 C. for 24 hours. The formaldehyde content of thereaction mixture was determined by the procedure in Example III aboveand found to be 1.02% by weight. The reaction mixture was then reactedat 50 C. to 52 C. for 17 additional hours. The formaldehyde content wasfound to be 0.01% by weight. The mixture was then cooled to roomtemperature and 70 g. of sulfuric acid (96% by weight active) and 70 g.of water were added. The reaction product was a suspension of solids insalt water. The solids were allowed to settle and the salt Water removedby decantation. The solids were then washed three times with 500 g.quantities of water cooled to 10 C. After the third wash, theformaldehyde content of the third wash water was determined and found tobe 0.01% by weight. After the methylolated crude sulfone mixture waswashed free of formaldehyde, it was analyzed by the De Jong method andfound to contain 1.8 free methylol groups per mole of sulfone.

230 g. of Z-naphthalene sulfonic acid mixture, which contained 0.66 moleof Z-naphthalene sulfonic acid and was about 75% by weight active, wasadded to the washed methylolated sulfone solids and the resultingreaction mixture refluxed at 110 C. for hours. The reaction mixture wasthen cooled to 30 C. and 375 g. of Water and 95 g. of 50% by weightsodium hydroxide solution were added. The resulting product was a clearsolution of a synthetic agent which contained 44% by weight solids andhad a pH of 2.2 as is. Analysis of the tanning agent by the De Jongmethod showed that it contained 0.4 methylol groups per mole of sulfoneemployed instead of the expected 0.7 methylol groups per mole ofsulfone. The unaccounted free methylol groups had reacted with thebyproducts present in the crude sulfone mixture. Such byproductsincluded polymeric sulfones, phenolic sulfonic acids an the like. Theagent precipitated from 2% by weight sodium chloride solution.

EXAMPLE VIII This example demonstrates the preparation of a synthetictanning agent from a dihydroxy dimethyl diphenyl sulfone prepared fromortho cresol.

A dihydroxy diphenyl sulfone was prepared from ortho cresol by using theprocedure given in Example I(A) above and substituting an equirnolarquantity of ortho cresol for phenol. The resulting dihydroxy dimethyldiphenyl sulfone was washed, filtered and dried. 139 g. (0.5 mole) ofthe dihydroxy dimethyl diphenyl sulfone obtained from this preparationwas mixed with 400 cc. water, 81 g. (1 mole) of formaldehyde solution(37% by weight) and 300 g. (0.86 mole) of Z-naphthalene sulfonic acidsolution (75% by weight active) prepared according to the procedure inExample II above. The resulting reaction mixture was refluxed at 102 C.for hours in a reaction vessel, cooled to 30 C. and neutralized to a pHof 2.8 by the addition of 171 g. of 50% by weight sodium hydroxidesolution. The mixture was cooled at 30-4 0 C. during neutralization. Theneutralized product was a synthetic tanning agent in the form of a clearsolution containing 38.4% by weight of synthetic tanning agent. Theproduct was analyzed by the De Iong method and found to contain 0.3 freemethylol groups per mole of sulfone employed.

EXAMPLE IX Evaluation of the synthetic tanning agents prepared inExamples III through VIII.

300 g. of drained pickled stock gauging 3 oz. and having a pH of 2.0 wasfloated in 300 cc. of a 4% by weight salt solution for 30 minutes torewet and soften the stock. The solution was drained. 150 g. of waterand 90 g. of the synthetic tanning agent obtained in Example III abovewas added. The stock was rotated for 4 hours in the synthetic tanningagent and water solution. After 4 hours of rotation, exhaust of thesynthetic tanning agent was complete. Exhaust was determined by theOflicial A.L.C.A. Method A2S. The exhausted solution was drained and anew float of 300 cc. of water and 24 g. of a chrome liquor containing25% chromium oxide of 33% basicity were added. The sample of stock wasrotated in this liquor for 12 hours. Then cc. of a 10% by weight sodiumbicarbonate solution was added and the sample was rotated for anadditional two hours. The sample was taken out of the drum, horsed for48 hours, then washed in fresh water, dyed and fat liquored in the usualmanner. After fat liquoring, the sample was taken out of the drum,dried, staked and toggled on frames. After drying, the leather samplewas finished in the usual manner. The leather sample produced by thisprocedure had a round feel and was soft and strong. The patterndeveloped on the grain of the leather by the above tanning procedure wascarefully examined. The pattern was found to be highly uniform, spreadevenly over all of the surface of the leather with high depth. N0coarseness whatsoever in the pattern was noted and the pattern gave anoverall picture of a natural, uniform, fine pattern. On strongstretching of the leather sample, the sample immediately recovered thesame pattern after the stretch was released.

The same test procedure was used to evaluate samples of the synthetictanning agents obtained in Examples IV through VIII. The followingresults were obtained. Stock tanned with the products of Examples IV andV by this procedure showed the same favorable results as obtained withthe product of Example III. The leather obtained with Example IV wassuperior to that obtained With the product of Example III and theproperties of the leather obtained with the product of Example V wereclosest in quality and properties to that obtained with the product ofExample IV. Leather tanned with the product of Example VI showed a verypoor and non-uniform shrinking pattern having low depth, poor surfacecoverage by the pattern and was inferior in feel and strength. Theleather obtained'with the product of Example VII was slightly better inappearance to that obtained with the product of Example VI but was veryinferior to the leather obtained with the product of Examples III, IVand V. Leather obtained with the product of Example VIII had a very poornon-uniform pattern. When the product of Example VI was neutralized to apH of 2.2 as is and the precipitated mixture was used in the evaluationon leather, equally poor results were obtained as with the unneutralizedproduct. It was noted that the precipitated tanning agent dissolvedgradually during the tanning procedure but that the gradual solution ofthe precipitated tanning agent did not improve the shrunken grainleather pattern. As pointed out above, the grain must be shrunken duringthe initial phase of the tanning process.

EXAMPLE X Shaved chrome tanned stock was partly dechromed with a 5% byWeight oxalic acid solution, washed thoroughly and then retained in a50% float by the procedure described in Example IX above with 30% byWeight of each of the synthetic tanning agents described in Examples IIIthrough VIII above. When the samples of finished shrunken grain leatherwere examined, the same results as those obtained in Example IX abovewere noted and the only distinction was that the differences between thevarious tanning agents were more pronounced. This meant that thesynthetic tanning agents produced in Examples IV and V were superior toall of the others. The leather obtained with the synthetic tanning agentof Example III was good and of excellent quality. Leather obtained fromExample VI was extremely poor. Leather obtained with the synthetictanning agents of Example VII and VIII respectively were also extremelypoor.

EXAMPLE XI 500 g. of shaved chrome calf leather was dechromed with anoxalic acid solution containing 25 g. oxalic acid in 500 g. water. Whenthe shrinkage temperature of the stock dropped from an original value of212 F. to F. the dechromed leather was washed thoroughly and thentreated in a tanning liquor containing 250 g. water with g. of thesynthetic tanning agent of Example IV. The leather samples were rotatedin this liquid for 5 hours. The tanning liquor was drained, the samplesreflected with 500 g. water and 40 g. of a chrome liquor containing 25%chromium oxide of 33% basicity was added. After 8 hours of rotation, 50g. of a 10% solution 17 of sodium bicarbonate was added as the leatherrotated for an additional half hour. The shrunken grain leather sampleswere washed, dyed, fat-liquored and finished in the usual way. A verydeep, fine and uniform pattern resulted, evenly distributed over theentire area of the calf skin. The same procedure was repeated with thesynthetic tanning agent of Example V with equally good results.

EXAMPLE XII 100 lbs. of pickled cowhides were floated in 200' lbs. of a4% by weight salt solution for one hour to soften the stock. The saltsolution was drained and 50 lbs. of water and 30 lbs. of the synthetictanning agent produced according to Example V above were added as atanning liquor. The hides were rotated for six hours until the exhaustof the synthetic tanning agent was complete. Subsequently, the tanningliquid was drained and the hides refloated in 100 lbs. water. 9 lbs. ofa chrome liquor containing 25% by weight chromium oxide of 40% basicitywas added. The hides were'rotated in this liquor for 12 hours. Then 0.8lb. of sodium bicarbonate dissolved in 8 lbs. water was added over aperiod of one-half hour and the hides rotated for an additional 2 hours.The hides were taken out from the drum, horsed for 48 hours, then washedin water, neutralized with sodium bicarbonate solution, dyed andfat-liquored in the usual Way. After this procedure was finished, thehides were taken out, dried, staked and toggled on frames. After drying,they were finished in the usual way. The appearance of the shrunkengrain leather produced by this procedure was examined. The leather had around feel and was soft and strong. The shrunken grain pattern on theleather was examined and found to show a uniform picture with nodifference in the pattern formed on the middle parts, neck parts, tailparts or flanks of the hides. The pattern was deep, very uniform, fineand natural looking. Even the most powerful stretching of the hides didnot make the pattern disappear and recovery of the pattern after releaseof the stretch was complete.

EXAMPLE XIII 10 lbs. of shaved chrome tanned side leather were partiallydechromed by treatment with a by weight oxalic acid solution. Thepartially dechromed hides were washed thoroughly and the wash water wasdrained. 5 lbs. of water and 3 lbs. of the synthetic tanning agent ofExample IV above were added as a tanning liquor and the hides wererotated in this liquor for 5 hours. The tanning liquor was drained and afloat of lbs. of water and 3 lbs. of a chrome liquor containing chromiumoxide of 33% basicity was added. The hides were rotated in this liquorfor 12 hours. Then 0.12 lb. of sodium bicarbonate dissolved in 1.2 lbs.water was added and the hides rotated for two additional hours. Thefloat was drained and 10 lbs. water and 1 lb. of a 35% quebracho extractwere added. The hides were rotated for five additional hours, thenwashed and finished in the usual way. The finished shrunken grainleather was examined and showed very high depths of the pattern formdistributed uniformly over the entire area of the hides. The feel of theleather was round. The shrunken grain pattern on the leather recoveredcompletely after release of stretching. The finished leather was softand strong.

EXAMPLE XIV This example demonstrates the preparation of a shrunkengrain synthetic tanning agent using 95% by weight pure dihydroxydiphenyl sulfone isomer mixture.

(A) Preparation of 95% by Weight pure dihydroxy diphenyl sulfone isomermixture.

1148 g. (12.2 moles) of phenol, 612 g. (6 moles) of sulfuric acid (96%by weight active) and 125 g. monochlorobenzene were charged into areaction vessel equipped'with an agitator and a water separation trap.The reaction mixture was heated to the reflux temperature which wasabout C. The escaping vapors of chlorobenzene and water formed duringthe reaction were condensed in the condenser and were separated in thewater trap. The dry chlorobenzene was returned to the reaction mixture.Reaction temperature was gradually increased to a temperature between C.and C. After from about 210 cc. to 215 cc. of water had been separatedby azeotropic distillation, the reaction mixture was titrated todetermine its acidity. A 10 g. sample of the reaction mixture at thispoint should not require more than 19.00 cc. to 20.00 cc. of 0.5 Nsodium hydroxide solution to neutralize the sample to a pH of 7.0.

After the desired acidity was obtained, 500 cc. of water was addedcarefully to the reaction product. The reaction product was thenneutralized to a pH between 5 and 6 by the cautious addition of fromabout 120 g. to about 130 g. of 50% by weight sodium hydroxide solution.Approximately 1,000 cc. of water was then added to the reaction productand the resulting mixture was azeotropically distilled to remove thechlorobenzene. After all of the chlorobenzene was stripped from thereaction mixture, an additional 1,000 cc. of water was added and theresulting solution of the reaction product was heated to its boilingpoint. A clear solution was obtained at the boiling point. The clearsolution was then transferred to a reaction vessel containingapproximately 4,000 cc. of boiling water and the resulting dilutesolution was allowed to cool slowly to room temperature with vigorousagitation. Dihydroxy diphenyl sulfone precipitated in the form of creamcolored crystals from the solution during cooling.

The precipitated crystals were filtered off on a filter press withoutwashing and dried at 105-110 C. The dry product was analyzed for itsactual sulfone content and found to contain 95 by weight of puredihydroxy sulfone isomers and 5% by weight of impurities. The isomers inthe mixture consisted of 4,4'-dihydroxy diphenyl sulfone and4,2-dihydroxy diphenyl sulfone. The 5% by weight of impurities in themixture included polymeric sulfones, phenol sulfonic acids, otherbyproducts and the like.

(B) Preparation of a shrunken grain synthetic tanning agent by using a95 by weight pure dihydroxy diphenyl sulfone isomer mixture.

164.5 g. of the 95% by weight pure sulfone isomer mixture obtained inpart (A) and containing 156 g. (0.625 mole) of dihydroxy diphenylsulfone isomers, 426 g. of water, 248 g. of 2-naphthalene sulfonic acidsolution containing 0.653 mole of sulfonic acid, 0.394 mole of sulfuricacid and the balance being water, and 101 g. aqueous formaldehydesolution containing 1.25 mole of formaldehyde were mixed together andheated to reflux. The molar ratio of formaldehyde to sulfone was 2 molesof formaldehyde to 1 mole of sulfone. The reflux temperature of themixture was 101.5 C. The refluxing solution was slightly hazy inappearance. After 15.5 hours of reflux, the reaction mixture was cooledto 40 C. and neutralized with 106 g. of 50% by weight sodium hydroxidesolution and 50 g. of water. No precipitate formed during theneutralization but the solution had a faint haze. 10 g. of filter aidwas added and the solution was filtered through a Knieger pressurefilter. It was then brilliantly clear. Analysis of the shrunken grainsynthetic tanning agent showed that it contained 0.9 molev of freemethylol groups per 1 mole of sulfone employed in the reaction. Theproperties of the tanning agent were comparable to the synthetic tanningagent of Example V above.

EXAMPLE XV This example demonstrates preparation of a shrunken grainsynthetic tanning agent by using a 100% by weight pure dihydroxydiphenyl sulfone isomer mixture. 2

The procedure given in Example IV above was repeated with the exceptionthat 117.5 g. (0.47 mole) of 100% by weight of a pure crystallinedihydroxy diphenyl sulfone isomer mixture prepared by the proceduregiven in part (B) of Example I above was employed instead of 154 g. ofsulfone paste. The sulfone isomers in the mixture were present in aweight ratio of 88% of the 4,4'-dihydroxy diphenyl sulfone isomer to 12%of the 4,2-dihydroxy diphenyl sulfone isomer. The properties of thesynthetic tanning agent were comparable to those of the synthetictanning agent produced in Example IV.

The foregoing examples demonstrate that the synthetic tanning agents ofthe present invention produce shrunken grain leathers having deep,uniform patterns which completely recover after stretching and releaseof the stretch.

The examples given below, that is, Examples XVI through XVIII furtherdemonstrate that synthetic tanning agent solutions prepared byprocedures outside the scope of the invention do not produce shrunkenleathers having satisfactory properties.

EXAMPLE XVI This example is directed to preparing a tanning agent froman impure, crude sulfone.

200 g. of a crude dihydroxy diphenyl sulfone isomer mixture was preparedaccording to the procedure given in Example VII above, the onlydifference being that the reaction was carried half way to completion.The crude sulfone contained 80% by weight solids, was about 40% pure byweight and contained 80 g. (0.32 mole) of dihydroxy diphenyl sulfoneisomers. The 60% by weight of impurities in the mixture includedpolymeric sulfones, phenol sulfonic acid, other byproducts and the like.This quantity of sulfone represented a 37% yield instead of the expected75% yield. The crude sulfone was mixed with 100 g. of water and 95 g.(1.17 mole) of aqueous formaldehyde solution 37% by weight active). Theratio of formaldehyde to sulfone was 3.66 moles of formaldehyde to 1mole of dihydroxy diphenyl sulfone. The mixture was heated to 50 C. andheld at 50 C. with agitation for 12 hours. After heating 12 hours at 50C., a gummy product precipitated from the solution. The water layer wasdecanted from the gummy resinous precipitate and the precipitate washedthree times with 500 cc. quantities of cold water. Analysis showed thatthe third 500 cc. water wash was free of formaldehyde, that is, theprecipitate did not contain any free or unreacted formaldehyde. Thecrude methylolated sulfone mixture contained 1.4 free methylol groupsper mole of sulfone employed.

125 g. (0.33 mole) of naphthalene sulfonic acid mixture (about 75% byweight active) prepared by the procedure described in Example II abovewas added to the washed resinous precipitate and then 50 g. of water wasadded. The resulting mixture was heated to reflux and refluxed for 2hours. No solubilization of the reactants occurred during the 2 hoursthat the reactants were refiuxed. Further, no appreciable solubilizationof the reactants were refiuxed. Further, no appreciable solubilizationof the reactants occurred on prolonged refluxing of the reactionmixture. After cooling the reaction mixture, the major portion of thereaction product formed a gummy resinous mass, which was insoluble inwater. Neutralization of the reaction product to a pH of 3.5 by theaddition of sodium hydroxide solution did not solubilize the resinousreaction product. Further, the reaction product was not soluble in asalt solution containing 0.1% by weight sodium chloride. The resinousproduct contained 0.0 free methylol groups per mole of sulfone employed.The product was not in suitable form for use as a synthetic tanningagent in producing shrunken grain leather.

This example demonstrated the use of a crude dihydroxy diphenyl sulfonemixture which had a purity of about 40% by weight and was outside thepurity limit of this invention did not give a satisfactory shrunkengrain tanning agent even though the quantities used, that is, one moleof the dihydr xy diph nyl sulfone mixture,

20 3.66 moles of formaldehyde and 1.06 moles of 2-naphthalene sulfonicacid, were within the limits of this invention.

EXAMPLE XVII This example is directed to the preparation of a tanningagent from a crude sulfone.

(A) 188 g. (2 mole) phenol, 102 g. (1 mole) sulfuric acid 98% by weightand 25 cc. chlorobenzene were heated to reflux and the water formedduring the reaction was removed azeotropically. After refluxing thereaction mixture for 75 minutes, the reflux temperature was 175 C. and atotal of 37 cc. of water had been removed by azeotropic distillation.The reaction mixture was neutralized with 13.5 g. of sodium hydroxideand 94 g. of water. The neutralized crude sulfone dissolved when themixture was heated to its boiling point. 200 cc. cold water was added tothe crude dihydroxy diphenyl sulfone. The crude sulfone isomer mixturewas 75% pure by weight. The 25% by Weight of impurities in the mixtureincluded polymeric sulfones, phenol sulfonic acids, other byproducts andthe like.

(B) 128 g. (1 mole) naphthalene was reacted with 160 g. (1.6 mole)sulfuric acid (98% by weight) for 1 hour at 155 C. The reaction mixturewas cooled to C. and 100 g. of ice was added to the reaction mixture atroom temperature. The reaction mixture was a mixture containing about75% by weight of 2-naphthalene sulfonic acid plus excess free sulfuricacid, that is, 1.0 mole of 2-naphthalene sulfonic acid and 0.6 mole ofsulfuric acid.

(C) The crude dihydroxy diphenyl sulfone mixture, which represented 0.75mole of 100% by weight pure dihydroxy diphenyl sulfone isomers obtainedin part (A) above was mixed with the solution of Z-naphthalene sulfonicacid (1.0 mole) obtained in part (B) above and 296 g. of water added. Atotal of 162 g. (2 moles) of aqueous formaldehyde solution (37% byweight active) was added and the resulting reaction mixture heated toreflux. The reaction mixture contained 0.75 mole of sulfone and 2.00moles of formaldehyde and had a molar ratio of formaldehyde to sulfoneof 2.67. The reactants in the reaction mixture did not dissolve in thereaction mixture but remained insoluble even after the reaction mixturehad been refluxed for 14 hours. When the reaction mixture was cooled andneutralized, a gummy precipitate was obtained. The reaction product wasinsoluble over the entire neutralization range, that is, from a pH ofabout 0 to about 7. Further, the final product was insoluble in saltsolutions containing as little as 0.1% by weight sodium chloride. Thefinal reaction product contained 0.0 methylol groups per mole of sulfoneemployed. This product was not in suitable form for use as a synthetictannin-g agent in producing shrunken grain leather.

This example demonstrated that use of a crude dihydroxy diphenyl sulfoneisomer mixture which had a purity of 75% by weight and was outside thepurity limits of this invention did not give a satisfactory shrunkengrain synthetic tanning agent even though the quantities used, that is,one mole of the dihydroxy diphenyl sulfone mixutre, 2.67 moles offormaldehyde and 1.33 moles of Z-naphthalene sulfonic acid, were withinthe limits of the present invention.

EXAMPLE XVIII This example is directed to preparing a tanning agent witha molar quantity of formaldehyde outside the limits of the presentinvention.

127.5 g. of a dry, crystalline dihydroxy diphenyl sulfone isomer mixtureof 98% purity by weight as described in Example I(A) above, g. (0.5mole) of 2-naphthalene sulfonic acid mixture as described below, 500 g.of water and 55 g. (0.68 mole) of aqueous form-. aldehyde solution (37%by weight active) were mixed and heated to reflux. The mixture ofsulfone isomers 21 weighed 125 g. (0.5 mole). The sulfone isomers in themixture were present in a weight ratio .of 88% of the 4,4'-dihydroxydiphenyl sulfone isomer to 12% of the 4,2'-dihydroxy diphenyl sulfoneisomer. The 2% by weight of impurities included polymeric sulfones,phenol sulfonic acids, other byproducts and the like. The naphthalenesulfonic acid was prepared by the procedure given in Example XVII(B)abovewith the exception that ice was ,not added and the sulfonic acidwas substantially anhydrous. After 18 hours at reflux, the mixture wasneutralized with 86 g. of 50% .by weight sodium hydroxide solution and100 g. of water to obtain a synthetic tanning agent solution having a pHof 2.5. The solution contained 30% by. weight solids. The molar ratio offormaldehyde to sulfone was 1.35:1 and the synthetic tanning agentcontained 0.36 free methylol groups per moleof sulfone employed, thatis, the tanning agent contained about 0.4 methylol groups per mole ofsulfone employed. The tanning agent wasevaluated as a shrunken graintanning agent for leather. The agent did not profew scattered patternson the leather and none of the patterns had depth. e

This example demonstrated that use of less than 1.5 moles offormaldehyde per mole of sulfone did not give a satisfactory shrunkengrain tanning agent because the agent contained less than 0.5 methylolgroups per mole of sulfone employed and was outside'the limits of thepresent invention. i

What is claimed is:

1. A process of producing shrunken grain leather from a skin selectedfrom the group consisting of animal skins, pickled skins, partiallytanned skins, partially dechromed skins and dechromed skins comprising(I) introducing from about by weight to about 50% by weight based on theweight of said skin of a water soluble shrunken grain synthetic tanningagent in substantially monomeric form comprising the reaction product of(a) one mole of a sulfone having a purity of from about 95% to 100% byweight selected from the group consisting of 4,4'-dihydroxy diphenylsulfone, 4,2-dihydroxy diphenyl sulfone, 2,2- dihydroxy diphenyl sulfoneand mixtures thereof, (b) from about 1.5 moles to about 5.0 moles offormaldehyde per mole of said sulfone, and (c) from about 0.5 mole toabout 2.0 moles of 2- naphthalene sulfonic acid per mole of saidsulfone, said (a), (b) and (0) being mixed at about room temperature,and thereafter reacted at temperatures of from about 20 C. to about 150C. in aqueous solution until a clear solution is obtained with theproviso that pressure is employed at temperatures between about 110 C.and about 150 C. and water being present in an amount of from aboutthree to about five times the weight of said sulfone, and with thefurther proviso that said reaction product contains at least 0.5 freemethylol groups per mole of said sulfone, is soluble in salt solutionscontaining at least 2.5% by weight of sodium chloride and when insolution does not precipitate on neutralization at a pH of from about 0to about 7, and from about by weight to about 100% by weight based onthe weight of said skin of water, and thereafter (II) drumming said skinwith said agent at a temperature of from about 70 F. to about 90 F. forabout 2 hours to about 12 hours so that said agent is exhausted intosaid skin. 2. A process of producing shrunkent grain leather from a skinselected from the group consisting of animal skins, pickled skins,partially tanned skins, partially dechromed skins and dechromed skinscomprising 2.0 duce satisfactory shrinking effects, that is, there were22 I (I) introducing from about 15% by weight to about 50% by weightbased on the weight of said skin of ,a water soluble. shrunken grainsynthetic tanning agent in substantially monomeric form comprising thereaction product of (a) one mole of a methylolated sulfone having apurity of from about 95 to 100% by weight selected from the groupconsisting of rnethylolated 4,4'-dihydroxy diphenyl sulfone,methylolated 4,2-dihydroxy diphenyl sulfone, methylolated 2,2-dihydroxydiphenyl sulfone and mixtures thereof wherein said sulfone contains fromabout 1.5 to about 4 free methylol groups per mole of said sulfone, saidmethylolated sulfone I being prepared by reacting about one mole of adisodium salt of dihydroxy diphenyl sulfone having a purity of fromabout 95% to 100% by 1 Weight selected from the group consisting of thedisodium salt of 4,4'-dihydroxy diphenyl sulfone, the disodium salt of4,2' -dihydroxy diphenyl sulfone, the disodium salt of 2,2'-dihydroxydiphenyl sulfone and mixtures thereof, and from about 1.5 moles to about5 moles of formaldehyde at about 20 C. to about 55 C. in water presentin an amount of from about one and onehalf to about two times the weightof said diphenyl sulfone and at a pH of about 9.5 to about 10, therebyforming the disodium salt of said methylolated sulfone. and thereafterprecipitating said methylolated sulfone by acidification of saiddisodium salt of said methylolated sulfone, and (b) from about 0.5 moleto about 2.0 moles of 2- naphthalene sulfonic acid per mole of saidsulfone, said (a) and (b) being mixed at about room temperature, andthereafter reacted at temperatures of from about 50 C. to about 150 C.in aqueous solution until a clear solution is obtained with the provisothat the pressure is employed at temperatures between about 110 C. andabout 150 C. and water being present in an amount of from about one-halfto about two times the weight of said sulfone, and with the furtherproviso that said reaction product contains at least 0.5 free methylolgroups per mole of said sulfone, is soluble in salt solutions containingat least 2.5% by weight of sodium chloride and when in solution does notprecipitate on neutralization at a pH of from about 0 to about 7, andfrom about 30% by weight to about 100% by weight of said skin of water,and thereafter (II) drumming said skin with said agent at a temperatureof from about 70 F. to about F. for about 2 hours to about 12 hours sothat said agent is exhausted into said skin.

3. Leather treated with a water soluble shrunken grain synthetic tanningagent in substantially monomeric form comprising the reaction product of(a) one mole of a sulfone having a purity of from about to by weightselected from the group consisting of 4,4'-dihydroxy diphenyl sulfone,4,2'-dihydroxy diphenyl sulfone, 2,2'-dihydroxy diphenyl sulfone andmixtures thereof,

(b) from about 1.5 moles to about 5.0 moles of formaldehyde per mole ofsaid sulfone, and

(c) from about 0.5 mole to about 2.0 moles of 2- naphthalene sulfonicacid per mole of said sulfone,

said (a), (b) and (c) being mixed at about room temperature, andthereafter reacted at temperatures of from about 20 C. to about 150 C.in aqueous solution until a clear solution is obtained with the provisothat pressure is employed at temperatures between about C. and about C.and water being present in an amount of from about three to about fivetimes the weight of said sulfone, and with the further proviso that saidreaction product contains at least 0.5 free methylol groups per mole ofsaid sulfone, is soluble in salt solutions containing at least 2.5% byweight of sodium chloride and when in solution does not precipitate onneutralization at a pH of from about to about 7 wherein said reactionproduct is drummed into said leather at a temperature of from about 70F. to about 90 F. for about 2 hours to about 12 hours so that saidreaction product is exhausted into said leather.

4. Leather treated with a water soluble shrunken grain synthetic tanningagent in substantially monomeric form comprising the reaction product of(a) one mole of a methylolated sulfone having a purity of from about 95%to 100% by Weight selected from the group consisting of methylolated4,4-dihydr0xy diphenyl sulfone, methylolated 4,2-dihydroxy' diphenylsulfone, methylolated 2,2-dihydroxy diphenyl sulfone and mixturesthereof wherein said sulfone contains from about 1.5 to about 4 freemethylol groups per mole of said sulfone, said methylolated sulfonebeing prepared by reacting about one mole of a disodium salt ofdihydroxy diphenyl sulfone having a purity of from about 95% to 100% byweight selected from the group consisting of the disodium salt of4,4-dihydroxy diphenyl sulfone, the disodium salt of 4,2-dihydroxydiphenyl sulfone, the disodium salt of 2,2'-dihydroxy diphenyl sulfoneand mixtures thereof, and from about 1.5 moles to about 5 moles offormaldehyde at about 20 C. to about 55 C. in water present in an amountof from about one and one-half to about two times the weight of saiddiphenyl sulfone and at a pH of about 9.5 to about 10, thereby formingthe disodium salt of said methylolated sulfone and thereafterprecipitating said methylolated sulfone by acidification of saiddisodium salt of said methylolated sulfone, and (b) from about 0.5 moleto about 2.0 moles of 2- naphthalene sulfonic acid per mole of saidsulfone, said (a) and (b) being mixed at about room temperature, andthereafter reacted at temperatures of from about C. to about 150 C. inaqueous solution until a clear solution is obtained with the provisothat pressure is employed at temperatures between about 110 C. and about150 C. and water being present in an amount of from about one-half toabout two times the weight of said sulfone, and with the further provisothat said reaction product contains at least 0.5 free methylol groupsper mole of said sulfone, is soluble in salt solutions containing atleast 2.5% by weight of sodium chloride and when in solution does notprecipitate on neutralization at a pH of from about 0 to about 7 whereinsaid reaction product is drummed into said leather at a temperature offrom about F. to about F. for about 2 hours to about 12 hours so thatsaid reaction product is exhausted into said leather.

References Cited UNITED STATES PATENTS 1,901,536 3/1933 Shafer.

FOREIGN PATENTS 750,143 6/1956 Germany.

LEON D. ROSDAL, Primary Examiner M. HALPERN, Assistant Examiner US. Cl.X.R. 260-512; 8-94.33

